An electric vehicle is a type of vehicle that includes a motor driven by electric energy stored in a battery and uses the entire or a portion of driving force of the motor as a power source. Today, the electric vehicle is classified into a pure electric vehicle (EV) which uses electric energy of the battery as the power source and a hybrid electric vehicle (HEV) which includes an internal combustion engine to charge the battery and/or drive the vehicle using power generated from the engine.
Generally, the electric vehicle uses a portion of braking force during braking of the vehicle to generate electricity and charges the generated electric energy in the battery. Accordingly, the electric vehicle uses a portion of kinetic energy by a driving speed of the vehicle as energy required to drive a generator to simultaneously implement a reduction in the kinetic energy (that is, reduction in the driving speed) and a generation of the electric energy. The braking method described above is referred to as a regenerative braking.
The electric energy may be generated during the regenerative braking by reversely driving a separate generator or the motor. By performing the control of the regenerative braking during the braking of the electric vehicle, it may be possible to improve a driving distance of the electric vehicle (e.g., increase the driving distance) and improve fuel efficiency of the hybrid electric vehicle and reduce an emission of harmful exhaust gas.
Referring to FIG. 1, the related art calculates a required braking force to calculate the regenerative braking (S10), calculates a pre-intervention motor torque using the required braking force (S20), and then calculates the regenerative braking using the pre-intervention motor torque (S30).
In a general condition in which there is no need to perform the shifting, an input torque of a transmission is controlled by adjusting the post-intervention motor torque and an output shaft torque of the transmission is determined by a profile of the pre-intervention motor torque by slips of a clutch and a brake element in the transmission. In many instances of the shifting, a torque of the output shaft of the transmission may be more accurately estimated by performing the control as described above and therefore drivability and fuel efficiency for a regenerative braking system may be substantially improved. However, the torque may be increased due to the slips of the clutch and the brake element in the transmission during shifting. Accordingly, the torque of the input shaft is reduced by the torque intervention to correspond to the torque of the output shaft of the transmission. Today, the shifting is performed by referring to the pre-intervention torque before the entry of the shifting during braking of the vehicle. Therefore, even when a braking intention of a driver is changed, the driver's intention is not reflected to the shifting (e.g., the shifting is not actually performed).
Referring to FIG. 2, even when the braking force is increased during the shifting, the regenerative braking is calculated using the pre-intervention motor torque and therefore the regenerative braking may be calculated incorrectly. In other words, when the braking starts during the shifting, a hybrid control unit (HCU) is configured to generate the pre-intervention motor torque since the driver's required braking is increased. However, since a transmission control unit (TCU) refers to the motor torque before the shifting, the braking force is lost and thus a pushing sense is generated. Accordingly, the related art calculates the regenerative braking using the pre-intervention motor torque even during the shifting to incorrectly determine an area in which the charging is not performed as the case in which the regenerative braking is performed.